Update styles to support collapsible nav (#9095)
In preparation for adding collapsible sections, cleans up the CSS
styling we apply to the nav.
The differences here are very subtle without collapsible sections
enabled. Note these screenshots show an increase in the secondary nav
font size (table of contents) which I subsequently fixed.
Before
<img width="1169" alt="Screenshot 2024-11-13 at 12 45 49 PM"
src="https://github.com/user-attachments/assets/10ea345f-73d3-430c-a6f0-8448e2471b60">
After
<img width="1169" alt="Screenshot 2024-11-13 at 12 45 29 PM"
src="https://github.com/user-attachments/assets/6c1af159-1684-4d00-b33d-c0a88b5e0aa9">
However, with collapsible sections you can see the bugs we're addressing
Before
<img width="1169" alt="Screenshot 2024-11-13 at 12 48 19 PM"
src="https://github.com/user-attachments/assets/7902791f-6c4d-4c84-b366-ba9c4bd96214">
After
<img width="1169" alt="Screenshot 2024-11-13 at 12 47 30 PM"
src="https://github.com/user-attachments/assets/6e0c4c7c-4a41-4dd5-a9f1-beabff965dbb">
